The ultimate objective of this program is to determine if there may be detrimental health effects with human marihuana use because of retention of cannabinoids. In previous in vivo studies we observed a long-retained metabolite in the livers, spleens and fat of rats 15 days after a single I.V. or chronic I.P. injection of C14 delta 8-THC or C14-delta 9-THC. Because of the low concentration of the metabolite to lipid contamination in the tissue, we were unable to satisfactorily isolate and purify this cannabinoid for MS or NMR analyses. We have since developed an in vitro liver microsomal system for producing this unknown metabolite in which a tenfold greater concentration of the parent compound (11-hydroxy-delta 8-THC or 11-hydroxy-delta 9-THC) can be used. The specific objective of this project is to produce this unidentified retained metabolite with the in vitro system so that it will be of sufficient quantity for ultimate purification and analyses by GC/MS and NMR.